AD7357 datasheet(11/20 Pages) AD

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Preliminary Technical Data

AD7357

Rev. PrF | Page 11 of 20

Intermodulation Distortion

With inputs consisting of sine waves at two frequencies, fa and

fb, any active device with nonlinearities creates distortion

products at sum and difference frequencies of mfa ± nfb where

m, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms

are those for which neither m nor n are equal to zero. For

example, the second-order terms include (fa + fb) and (fa − fb),

while the third-order terms include (2fa + fb), (2fa − fb), (fa +

2fb), and (fa − 2fb).

The AD7357 is tested using the CCIF standard where two input

frequencies near the top end of the input bandwidth are used.

In this case, the second-order terms are usually distanced in

frequency from the original sine waves, while the third-order

terms are usually at a frequency close to the input frequencies.

As a result, the second- and third-order terms are specified

separately. The calculation of the intermodulation distortion is

as per the THD specification, where it is the ratio of the rms

sum of the individual distortion products to the rms amplitude

of the sum of the fundamentals expressed in decibels.

Thermal Hysteresis

Thermal hysteresis is defined as the absolute maximum change

of reference output voltage after the device is cycled through

temperature from either

T_HYS+ = 25°C to TMAX to 25°C

T_HYS– = 25°C to TMIN to 25°C

It is expressed in ppm using the following equation:

)

(

)

(

)

(

)

(

−

HYS

ppm

REF

HYS

where:

VREF(25°C) is VREF at 25°C

VREF(T_HYS) is the maximum change of VREF at T_HYS+ or

T_HYS–.

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